Is this a fair or biased sample. A store owner wants to survey customers about the products he sells. He programs the computer to select 100 customers from the mailing list and sends them each a survey.

(I'm torn on this one because on one hand, he's only selecting customers from his mailing list which makes me think biased, on the other he is using the computer to randomly select them so that seems fair. Also, of the people who are sent the surveys, everyone may not apply. So I'm leaning towards biased.)